Color hash keys (w/ specs)

[skull-squadron]

Supersedes #58

[gerrywastaken]

@steakknife Thanks heaps for the pull request and for updating the tests.

While testing your PR I ran into a bug that had previously slipped through. Fixed here:
#267

However your change means that code will once again not work correctly as it expects a symbol to begin with a colon. If plain_single_line starts adding color strings, then symbol? no longer will return true which will break the ruby19_syntax option. There's probably a really easy way to fix all this, but I can't think of it right now.

Also the name plain_single_line suggests options[:plain] = true and options[:multiline] = false. If we want a method that just does a options[:multiline] = false then perhaps it's better to create a new method that does only that and call it single_line leaving plain_single_line unmodified.

What are your thoughts?

[skull-squadron]

This was a quick hack to highlight an issue. Whichever way forward colorizes / formats keys of hashes by default seems like an obvious, desirable fix. If you know how to fix / refactor it (not switch to plain for keys?) and colorize keys, by all means, please supersede this PR.

EDIT: it also looks like the colorizing code is impure and this option save/restore state may run into nasty side-effects, and might want to pass a copy of options (or state) as a parameter as it's traversing composite objects during ai.

Leaving this open as a reminder would probably be good to prevent falling between the cracks. (And a later fix would close this and #58.)

[gerrywastaken]

@steakknife That's fine with me. I've got a few things on my plate at the moment, but I also like the idea behind this PR, so I'll come back to it, but it might not be soon. Thanks for the insight btw.